And, the standard pressure ratings for water, at 73°F (23°C), which are commonly recognized by DR-PR standard specifications for PE pipe, are as follows: 250; 200; 160; 125; 100; 80; 63; 50; and 40 psig. However, individual standards generally only cover a selected portion of this broad range.

The result of the use of these standard preferred number values is that a pipe’s standard pressure rating (PR) is a consistent result, independent of pipe size, which simply depends on its standard dimension ratio and the standard HDS of the material from which the pipe was made. This relationship is shown below:

Standard Pressure Ratings for Water, at 73°F (23°C), for SDR-PR Pipes, psig

Important:

Pipes with a lower SDR can withstand higher pressures.

4.13.Pressure Rating

For the purposes of pressure pipe design, the pipe’s pressure rating (PR) is determined by the hydrostatic design stress (HDS) that is assigned to the material from which the pipe is made.

x For example, HDPE (PE4710) DR 17 pipe has a static pressure rating for water of 125 psig.

x OD controlled pressure pipes are pressure rated per ASTM F714 using the formula below.

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Where:

PR = Pressure Rating, psi

HDS = Hydrostatic Design Stress at 73°F, psi (refer vendor info)

Af = Environmental Application Factor, Af = 1 for Water: Aqueous solutions of salts, acids and bases, Sewage, Wastewater, Alcohols, Glycols (anti-freeze solutions) etc. and Af = 0.5 for Fluids such as solvating/permeating chemicals in pipe or soil (typically hydrocarbons) in >2% concentrations, crude oil, fuel oil etc.

fT = Service Temperature Design Factor, fT = 1 for ≤ 80°F (27°C), fT = 0.8 for ≤ 100°F (38°C); fT = 0.63 for ≤ 120°F (49°C) and fT =

0.5 for ≤ 140°F (60°C)

DR = OD Controlled Pipe Dimension Ratio

x Working Pressure Rating

The working pressure rating (WPR) is based on the actual system requirements and is a pressure rating for pipe with flowing water. The WPR includes an allowance for water hammer surge pressures.

At a daily recurring average flow surge velocity of 5 fps and at 80°F, the working pressure rating of HDPE (PE4710) DR 17 pipe is also125 psig; similarly, the working pressure rating for PVC DR 18 is 120 psig (reference - AWWA C900-07, Equation 4). As such, PE 4710 has a higher working pressure rating than PVC at these common conditions.

The table below provides Pressure Rating and Allowable Total Pressure during Surge for PE4710 pipe at 80°F.

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(Source Reference - AWWA C901-08)

4.14.Plastic Pipe De-rating

The pressure rating of a plastic pipe is determined at 73.4°F. The strength of a plastic pipe decreases as the fluid temperature becomes warmer and therefore the plastic pipe needs to be de-rated for higher temperatures. The table below shows a derating factor for the increase in fluid temperature.

For example, the maximum working pressure for PVC piping is above 150 psig for all pipe sizes through 8 inches in diameter, but this is only for temperatures of 73.4°F. Any temperature above 73.4°F will result in a reduced working pressure within the piping system up to a maximum of 140°F. At this temperature the de-rating factor is 0.23, where it is 1.0 at 73°F.

4.15.Plastic Pipe Standards

Pipe manufacturers follow requirements set by the American Society of Testing Materials (ASTM) or American Water Works Association (AWWA) for specific pipe materials. Specification standards cover the manufacture of pipes and specify parameters such as internal diameters, loadings (classes), and wall thicknesses (schedules). The methods of pipe construction vary greatly with the pipe materials.

Poly vinyl chloride (PVC) Pipe

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PE pipe can withstand impact much better than PVC pipe, especially in cold weather installations where other pipes are more prone to cracks and breaks. Because heat fused PE joints are as strong as the pipe itself, it can be joined into long runs conveniently above ground and later, installed directly into a trench or pulled in via directional drilling or by using the re-liner process.

Many of the PE resins used in PE pipes are stress rated not only at the standard temperature, 73°F, but also at an elevated temperature, such as 140°F. Typically, PE materials retain greater strength at elevated temperatures compared to other thermoplastic materials such as PVC. At 140°F, PE materials retain about 50% of

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